The invention pertains to a drill pipe fabrication method, the resulting drill pipe, and an adapter member used in said method and drill pipe. Conventional drill pipe is formed in elongated sections, each section having pipe connections at both ends so that the drill pipe sections can be connected to one another in end-to-end relation to form a drill string. Typically, the pipe connections comprise tapered threads, each pipe section having a female connection or box at one end and a male connection or pin at the other end. Such drill pipe is used not only in apparatus for drilling wells of various types, but also in various types of mining or excavating devices, such as raise drills. While the well drilling equipment is typically designed to drill a relatively long but small diameter well bore, the mining equipment is typically used to form a shorter but relatively large diameter bore, such as a raise. The latter type of excavation is used, for example, in underground mines to connect tunnels located at different levels, and is necessarily of sufficiently large diameter to be used for moving various types of equipment and even personnel, from one level to the next.
Because of the substantial differences in the types, sizes, and environments of the bores which they are intended to form, there are numerous differences in these various types of drilling equipment. However, there are also certain similarities. The most significant, for present purposes, is the fact that each includes a drill bit which is supported by a string of drill pipe such as is described above. Likewise, while the dimensions, weight, and other parameters of the drill pipe may differ substantially depending upon the type of machine on which it is to be used, certain fabrication techniques have become conventional in the manufacture of virtually all types of drill pipe. More specifically, the end portions of the drill pipes which define the threaded pipe connections are known as "tool joints" and are frequently manufactured separately from the elongate central portion, which will be referred to herein as the "pipe body." The tool joints are then rigidly mounted on opposite ends of the pipe body by the manufacturer to form a complete section of drill pipe.
In the past, the most common technique for mounting the tool joints on the pipe bodies was through the use of threaded shrink grip connections. In this method the ends of the pipe body would be internally and/or externally upset so that threaded shrink grip formations could be machined thereon. Each tool joint would have one end machined to form a conventional threaded pipe connection for joining one section of drill pipe to another, while the other end would be machined to form a shrink grip type thread formation for cooperation with that of the pipe body. Assuming that the male shrink grip thread was formed on the pipe body, and the female shrink grip thread on the tool joint, the latter would be slightly undersized so that the connection between the two could not be made until the tool joint was heated sufficiently to cause a desired amount of thermal expansion. The joint thus heated would be threaded onto the pipe body and then quenched so that, as it cooled, it would shrink onto the pipe body upset, forming a tight, rigid, sealed connection.
This technique has several disadvantages. One of these is that the machining of the upset portion of the pipe body must be extremely precise. Thus, any machining errors or subsequent damage to the machined pipe body upset make it necessary to scrap the entire pipe body. This type of waste is quite expensive even if the error or damage occurs on the first end of the pipe body machined, and even more expensive if it occurs on the second end after the first has been properly finished. Furthermore, even without such errors and damage, such precise machining of a relatively large work piece such as a pipe body is in itself an expensive operation.
For these and other reasons, it has now become more common to weld the tool joints to the pipe body. As previously mentioned, the earlier pipe bodies designed to have the tool joints attached by shrink grip connections would be provided with upset end portions. Pipe bodies designed to have the tool joints attached by welding are also provided with upset end portions, but of a significantly smaller size. Due to the current predominance of welding tool joint connections, such small sizes have now become standard. Nevertheless, there are still a significant number of instances in which the shrink grip type tool joint is desired and requested by a customer. For example, this type of drill pipe may be preferred because, if the pipe body should fail, the tool joint can be more easily salvaged if it has been attached by the shrink grip method. However, since the smaller size pipe body upsets which have now become standard are too small to be machined for a proper shrink grip connection, it is necessary that pipe bodies having the larger, older style upsets be specially ordered and manufactured where a shrink grip tool joint is desired. Thus, it is difficult to provide such drill pipe at a reasonable cost.